DESCRIPTION: This research program will investigate the photochemical mechanism by which visual pigments are transformed from an inactive state to a state which interacts with other extrinsic membrane proteins in visual receptors. The primary experimental tool which will be used in these studies is time-resolved absorption spectroscopy to investigate spectra and kinetics of intermediate species produced on time scales from nanoseconds to seconds following light absorption. Native bovine rhodopsin will be studied under a variety of conditions, as well artificial rhodopsins in which the native retinal chromophore is replaced by synthetically modified retinals. Rhodopsin variants in which specific protein residues are changed will also be studied. In addition to these bovine pigments, studies will be carried out on native and modified cone pigments, on mutant forms of pigments from drosophila, and on human rhodopsin. By studying the spectra and kinetics of pigments with this wide range of chromophore and protein residue substitutions, Dr. Kliger and coworkers hope to gain an understanding of the mechanism of rhodopsin function at a molecular level, and achieve a better perspective on how chromophore-protein interactions mediate the visual excitation process.